Java DOM XML Parser

DOM parser parses the entire XML document and loads it into memory; then models it in a “TREE” structure for easy traversal or manipulation.

In short, it turns a XML file into DOM or Tree structure, and you have to traverse a node by node to get what you want.

Warning
DOM Parser is slow and consumes a lot of memory when it loads an XML document which contains a lot of data. Please consider SAX parser as solution for it, SAX is faster than DOM and use less memory.

1.0 How to read XML file in Java

/Users/mkyong/staff.xml

<?xml version="1.0"?>
<company>
    <staff id="1001">
        <firstname>yong</firstname>
        <lastname>mook kim</lastname>
        <nickname>mkyong</nickname>
        <salary>100000</salary>
    </staff>
    <staff id="2001">
        <firstname>low</firstname>
        <lastname>yin fong</lastname>
        <nickname>fong fong</nickname>
        <salary>200000</salary>
    </staff>
</company>

ReadXMLFile.java

package com.mkyong.seo;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;
import java.io.File;

public class ReadXMLFile {

  public static void main(String argv[]) {

    try {

    File fXmlFile = new File("/Users/mkyong/staff.xml");
    DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
    Document doc = dBuilder.parse(fXmlFile);

    //optional, but recommended
    //read this - http://stackoverflow.com/questions/13786607/normalization-in-dom-parsing-with-java-how-does-it-work
    doc.getDocumentElement().normalize();

    System.out.println("Root element :" + doc.getDocumentElement().getNodeName());

    NodeList nList = doc.getElementsByTagName("staff");

    System.out.println("----------------------------");

    for (int temp = 0; temp < nList.getLength(); temp++) {

        Node nNode = nList.item(temp);

        System.out.println("\nCurrent Element :" + nNode.getNodeName());

        if (nNode.getNodeType() == Node.ELEMENT_NODE) {

            Element eElement = (Element) nNode;

            System.out.println("Staff id : " + eElement.getAttribute("id"));
            System.out.println("First Name : " + eElement.getElementsByTagName("firstname").item(0).getTextContent());
            System.out.println("Last Name : " + eElement.getElementsByTagName("lastname").item(0).getTextContent());
            System.out.println("Nick Name : " + eElement.getElementsByTagName("nickname").item(0).getTextContent());
            System.out.println("Salary : " + eElement.getElementsByTagName("salary").item(0).getTextContent());

        }
    }
    } catch (Exception e) {
    e.printStackTrace();
    }
  }

}

Result:

Root element :company
----------------------------

Current Element :staff
Staff id : 1001
First Name : yong
Last Name : mook kim
Nick Name : mkyong
Salary : 100000

Current Element :staff
Staff id : 2001
First Name : low
Last Name : yin fong
Nick Name : fong fong
Salary : 200000

Looping the Node
ReadXMLFile2.java

package com.mkyong.seo;

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class ReadXMLFile2 {

  public static void main(String[] args) {

    try {

    File file = new File("/Users/mkyong/staff.xml");

    DocumentBuilder dBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();

    Document doc = dBuilder.parse(file);

    System.out.println("Root element :" + doc.getDocumentElement().getNodeName());

    if (doc.hasChildNodes()) {
        printNote(doc.getChildNodes());
    }
    } catch (Exception e) {
    System.out.println(e.getMessage());
    }
  }

  private static void printNote(NodeList nodeList) {
    for (int count = 0; count < nodeList.getLength(); count++) {
    Node tempNode = nodeList.item(count);

    // make sure it's element node.
    if (tempNode.getNodeType() == Node.ELEMENT_NODE) {

        // get node name and value
        System.out.println("\nNode Name =" + tempNode.getNodeName() + " [OPEN]");
        System.out.println("Node Value =" + tempNode.getTextContent());

        if (tempNode.hasAttributes()) {

            // get attributes names and values
            NamedNodeMap nodeMap = tempNode.getAttributes();

            for (int i = 0; i < nodeMap.getLength(); i++) {
                Node node = nodeMap.item(i);
                System.out.println("attr name : " + node.getNodeName());
                System.out.println("attr value : " + node.getNodeValue());
            }
        }

        if (tempNode.hasChildNodes()) {
            // loop again if has child nodes
            printNote(tempNode.getChildNodes());
        }
        System.out.println("Node Name =" + tempNode.getNodeName() + " [CLOSE]");
    }
    }
  }
}

2.0 How to modify XML file in Java

修改前xml file
file.xml

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<company>
   <staff id="1">
    <firstname>yong</firstname>
    <lastname>mook kim</lastname>
    <nickname>mkyong</nickname>
    <salary>100000</salary>
   </staff>
</company>

修改后xml

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<company>
   <staff id="2">
    <lastname>mook kim</lastname>
    <nickname>mkyong</nickname>
    <salary>2000000</salary>
        <age>28</age>
   </staff>
</company>

ModifyXMLFile .java修改xml

import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class ModifyXMLFile {

    public static void main(String argv[]) {

       try {
        String filepath = "c:\\file.xml";
        DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
        Document doc = docBuilder.parse(filepath);

        // Get the root element
        Node company = doc.getFirstChild();

        // Get the staff element , it may not working if tag has spaces, or
        // whatever weird characters in front...it's better to use
        // getElementsByTagName() to get it directly.
        // Node staff = company.getFirstChild();

        // Get the staff element by tag name directly
        Node staff = doc.getElementsByTagName("staff").item(0);

        // update staff attribute
        NamedNodeMap attr = staff.getAttributes();
        Node nodeAttr = attr.getNamedItem("id");
        nodeAttr.setTextContent("2");

        // append a new node to staff
        Element age = doc.createElement("age");
        age.appendChild(doc.createTextNode("28"));
        staff.appendChild(age);

        // loop the staff child node
        NodeList list = staff.getChildNodes();

        for (int i = 0; i < list.getLength(); i++) {

                   Node node = list.item(i);

           // get the salary element, and update the value
           if ("salary".equals(node.getNodeName())) {
            node.setTextContent("2000000");
           }

                   //remove firstname
           if ("firstname".equals(node.getNodeName())) {
            staff.removeChild(node);
           }

        }

        // write the content into xml file
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(doc);
        StreamResult result = new StreamResult(new File(filepath));
        transformer.transform(source, result);

        System.out.println("Done");

       } catch (ParserConfigurationException pce) {
        pce.printStackTrace();
       } catch (TransformerException tfe) {
        tfe.printStackTrace();
       } catch (IOException ioe) {
        ioe.printStackTrace();
       } catch (SAXException sae) {
        sae.printStackTrace();
       }
    }
}

3.0 How to create XML file in Java

要生成的xml file.xml

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<company>
    <staff id="1">
        <firstname>yong</firstname>
        <lastname>mook kim</lastname>
        <nickname>mkyong</nickname>
        <salary>100000</salary>
    </staff>
</company>

WriteXMLFile .java

package com.mkyong.core;

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class WriteXMLFile {

    public static void main(String argv[]) {

      try {

        DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

        // root elements
        Document doc = docBuilder.newDocument();
        Element rootElement = doc.createElement("company");
        doc.appendChild(rootElement);

        // staff elements
        Element staff = doc.createElement("Staff");
        rootElement.appendChild(staff);

        // set attribute to staff element
        Attr attr = doc.createAttribute("id");
        attr.setValue("1");
        staff.setAttributeNode(attr);

        // shorten way
        // staff.setAttribute("id", "1");

        // firstname elements
        Element firstname = doc.createElement("firstname");
        firstname.appendChild(doc.createTextNode("yong"));
        staff.appendChild(firstname);

        // lastname elements
        Element lastname = doc.createElement("lastname");
        lastname.appendChild(doc.createTextNode("mook kim"));
        staff.appendChild(lastname);

        // nickname elements
        Element nickname = doc.createElement("nickname");
        nickname.appendChild(doc.createTextNode("mkyong"));
        staff.appendChild(nickname);

        // salary elements
        Element salary = doc.createElement("salary");
        salary.appendChild(doc.createTextNode("100000"));
        staff.appendChild(salary);

        // write the content into xml file
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(doc);
        StreamResult result = new StreamResult(new File("C:\\file.xml"));

        // Output to console for testing
        // StreamResult result = new StreamResult(System.out);

        transformer.transform(source, result);

        System.out.println("File saved!");

      } catch (ParserConfigurationException pce) {
        pce.printStackTrace();
      } catch (TransformerException tfe) {
        tfe.printStackTrace();
      }
    }
}

4.0 How to count XML Elements in Java

file.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<company>
    <staff id="1">
        <firstname>yong</firstname>
        <lastname>mook kim</lastname>
        <nickname>mkyong</nickname>
        <salary>2000000</salary>
        <age>29</age>
    </staff>
    <staff id="2">
        <firstname>low</firstname>
        <lastname>yin fong</lastname>
        <nickname>fong fong</nickname>
        <salary>1000000</salary>
    </staff>
    <staff id="3">
        <firstname>Ali</firstname>
        <lastname>Baba</lastname>
        <nickname>Alibaba</nickname>
        <salary>199000</salary>
        <age>40</age>
    </staff>
</company>

CountXMLElement.java

import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class CountXMLElement {

  public static void main(String argv[]) {

    try {
        String filepath = "c:\\file.xml";
        DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
        Document doc = docBuilder.parse(filepath);

        NodeList list = doc.getElementsByTagName("staff");

        System.out.println("Total of elements : " + list.getLength());

    } catch (ParserConfigurationException pce) {
        pce.printStackTrace();
    } catch (IOException ioe) {
        ioe.printStackTrace();
    } catch (SAXException sae) {
        sae.printStackTrace();
    }
  }
}

5.0 解析网络xml

AlexaSEO.java

package com.mkyong.seo;

import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

public class AlexaSEO {

    public static void main(String[] args) {

        AlexaSEO obj = new AlexaSEO();
        System.out.println("Ranking : " + obj.getAlexaRanking("mkyong.com"));

    }

    public int getAlexaRanking(String domain) {

        int result = 0;

        String url = "http://data.alexa.com/data?cli=10&url=" + domain;

        try {

            URLConnection conn = new URL(url).openConnection();
            InputStream is = conn.getInputStream();

            DocumentBuilder dBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = dBuilder.parse(is);

            Element element = doc.getDocumentElement();

            NodeList nodeList = element.getElementsByTagName("POPULARITY");
            if (nodeList.getLength() > 0) {
                Element elementAttribute = (Element) nodeList.item(0);
                String ranking = elementAttribute.getAttribute("TEXT");
                if(!"".equals(ranking)){
                    result = Integer.valueOf(ranking);
                }
            }

        } catch (Exception e) {
            System.out.println(e.getMessage());
        }

        return result;
    }
}